1. Field of the Invention
This invention relates to seatbelt systems which restrain and protect passengers during vehicle emergencies and more particularly, to locking devices for such seatbelt systems.
2. Prior Art
Generally, seatbelt systems are designed such that one end of the passenger-restraining belt is retracted with a specific amount of force on a retractor fastened to the vehicle so that tension is always placed on an intermediate portion of the seatbelt. This tension causes the intermediate portion of the seatbelt to press against the body of the passenger so that the passenger is in a seatbelt-fastened condition. Furthermore, when the passenger removes the seatbelt, the seatbelt is automatically retracted and stored.
Recently, however, the low percentage of passenger use has led to the use of the so-called passive seatbelt systems which force the passenger to wear the seatbelt after entering the vehicle. Such passive seatbelt systems are arranged such that when the passenger enters the vehicle, the seatbelt is caused to move toward the front of the vehicle so that a sufficient space for the passenger to enter or leave the vehicle is formed between the seatbelt and the passenger seat. When the passenger slides his body into the space so that he is seated, the seatbelt is caused to move back toward the passenger seat. Accordingly, the space in front of the passenger contracts so that an intermediate portion of the seatbelt is fastened around the passenger thereby automatically placing the passenger in a seatbelt fastened condition. If the vehicle is involved in an emergency such as a collision and the seatbelt has been fastened around the passenger, a pawl actuated by an inertia sensor is caused to engage with ratchet wheels fastened to the seatbelt retractor shaft inside the retractor so that the rotation of the retractor shaft in the direction of seatbelt extension is abruptly stopped. Accordingly, extension of the webbing is prevented and the passenger is restrained.
In such passive seatbelt systems, however, the seatbelt is caused to move a great distance when the passenger enters or leaves the vehicle. As a result, the amount of seatbelt retracted on the retractor is extremely large in comparison to the amount retracted in an ordinary seatbelt systems. For this reason, the webbing retracted on the retractor shaft continues to be extended even after the rotation of the retractor shaft in the dirction of the seatbelt extension has been stopped during a vehicle emergency. The extension continues until the seatbelt is tightly wound on the retractor shaft. In other words, the seatbelt is tightened on the retractor shaft so that a length of seatbelt corresponding to the amount by which the seatbelt is tightened is continued to be extended from the retractor. As a result, such passive seatbelt systems suffer from a drawback of incomplete passenger restraint.